Re: [patch] futex API cleanups, futex-api-cleanup-2.5.69-A2

Rusty Russell (rusty@rustcorp.com.au)
Tue, 20 May 2003 10:15:23 +1000

In message <Pine.LNX.4.44.0305191752130.13233-100000@localhost.localdomain> you
write:
>
> > > - start the phasing out of FUTEX_FD. This i believe is quite unclean and
> > > unrobust, [...]
>
> FUTEX_FD is an instant DoS, it allows the pinning of one page per file
> descriptor, per thread. With a default limit of 1024 open files per
> thread, and 256 threads (on a sane/conservative setup), this means 1 GB of
> RAM can be pinned down by a normal unprivileged user.

Yes. There was a patch which limited it, never got applied.

The real solution is not to pin the page: I pinned the page originally
to prevent dealing with addresses changing due to swap out, but you
found the COW bug and that blew away that theory anyway 8)

I think the vcache callbacks or similar could be extended to cover the
swap out/swap in case.

Cheers,
Rusty.

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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